1. Field of the Invention
The present invention relates to a video reproducing apparatus. More specifically, the present invention relates to a video reproducing apparatus adapted for reproducing a television signal of two or more television standard systems.
2. Description of the Prior Art
Major television standard systems currently adopted in the world comprise the NTSC system and the PAL system. According to the NTSC system, the three primary colors are transmitted after conversion thereof into a brightness signal E.sub.Y and two chroma signals E.sub.I and E.sub.Q rather than direct transmission of the three primary color signals and these chroma signals as well as the brightness signal are used to provide color demodulation on the part of a receiver. As a result, compatibility of color television broadcasting with monochrome television broadcasting can be established. According to the NTSC system, the color subcarrier frequency f.sub.S is selected to be 3.58 MHz (more correctly, 3.579545 MHz) and the vertical reference frequency f.sub.V is selected to be 59.94 Hz. On the other hand, according to the PAL system, one out of the two chroma signals E.sub.I and E.sub.Q of the NTSC system is subjected to phase inversion for every other scanning line in transmission of the signals. According to the PAL system, the color subcarrier frequency f.sub.S is selected to be 4.43 MHz (more correctly, 4.43361875 MHz) and the vertical reference frequency f.sub.V is selected to be 50.00 Hz.
On the other hand, a carrier chroma signal low frequency region converting and multiple recording system (simply referred to as M system) has been proposed and put into practical use as one of the systems for recording a video signal in a magnetic tape in a video tape recorder and in particular the M system has been widely used in a home use video tape recorders. According to the M system, in the case of a video tape recorder of the NTSC system, for example, a color signal of the color subcarrier frequency f.sub.S of 3.58 MHz is converted into a low regional frequency of 629 KHz while a brightness signal is subjected to FM modulation, whereupon both are multiplexed and recorded in a magnetic tape. On the occasion of reproduction, the low regional converted color subcarrier frequency f.sub.SL of 629 KHz is converted into the color subcarrier frequency f.sub.S of 3.58 MHz. In the case of a video tape recorder of the PAL system, the low regional converted color subcarrier frequency f.sub.SL is selected to be 627 KHz and the color subcarrier frequency f.sub.S is selected to be 4.43 MHz. As described in the foregoing, the color subcarrier frequencies of the NTSC system and the PAL system are largely different in that the former is 3.58 MHz and the latter is 4.43 MHz. Accordingly, it follows that connection of a video tape recorder of the NTSC system to a monitor television receiver for use in a region where the
system has been adopted as the television standard system does not provide normal operation, and similarly, an attempt at reproduction of a magnetic tape recorded in accordance with the NTSC system using a video tape recorder of the PAL system does not result in normal operation, and vice versa. A so-called 4.43 NTSC system has been proposed and put into practical use as one of the systems for solving the above described problems. The 4.43 NTSC system is adapted to make possible reproduction of a magnetic tape recorded in accordance with the NTSC system using a video tape recorder of the PAL system. To that end, the color subcarrier frequency f.sub.S of a composite video signal obtained from the video tape recorder is selected to be 4.43 MHz. Accordingly, with a video tape recorder adapted to be capable of reproducing both the NTSC system and the 4.43 NTSC system, a magnetic tape recorded in accordance with the NTSC system can be reproduced in both an area where the NTSC system has been adopted and an area where the PAL system has been adopted as the television standard system.
FIG. 1 is a block diagram showing a conventional video tape recorder adapted to be capable of operating according to both the NTSC system and the 4.43 NTSC system. Referring to FIG. 1, a magnetic tape 1 is adapted to travel around a rotational drum 2. The rotational drum 2 is provided with rotational heads 3a and 3b and magnets 4a and 4b. A fixed head 6 is provided at the position for detecting the magnets 4a and 4b. A motor 5 is mechanically coupled to the rotational drum 2. The output of the fixed head 6 is connected to one input of a servo circuit 7. The outputs of the rotational heads 3a and 3b are coupled through a rotary transformer, not shown, to a common contact m of a switch SW1 in a color signal processing circuit 11 and the input portion of the brightness signal processing circuit 12. A contact a of the switch SW1 is connected to one input of an NTSC color signal processing circuit 11a and a contact b of the switch SW1 is connected to one input of a 4.43 NTSC color signal processing circuit 11b. On the other hand, the output of an oscillating circuit 9 having a crystal resonator C1 coupled thereto is connected to an input of a frequency divider 8. Furthermore, a frequency division ratio setting circuit 15a is connected to the frequency divider 8. The output of the frequency divider 8 is connected to the other input of the servo circuit 7 and the output of the servo circuit 7 is connected to the motor 5. A color reference signal generating circuit 10 comprises an oscillating circuit 10a, which is adapted to be switchably connected to a crystal resonator C2 or C3 through a switch SW2. The output of the oscillating circuit 10a is connected to the other input of each of the NTSC color signal processing circuit 11a and the 4.43 NTSC color signal processing circuit 11b. The outputs of the NTSC color signal processing circuit 11a, the 4.43 NTSC color signal processing circuit 11b and the brightness signal processing circuit 12 are connected to the input of a mixing circuit 13 and the output of the mixing circuit 13 is connected to a terminal 14.
When the rotating drum 2 is rotated by the motor 5, the rotating heads 3a and 3b reproduce a video signal recorded on the magnetic tape 1 and a reproduced signal S1 is provided. The reproduced signal S1 comprises a color signal and a brightness signal. The fixed head 6 detects the positions of the magnets 4a and 4b, thereby to provide a pulse signal S7. On the other hand, the oscillation frequency of the crystal resonator C1 is selected to be 3.579545 MHz and the oscillating circuit 9 provides a signal of the above described frequency. The frequency divider 8 frequency divides the above described signal, thereby to provide a vertical reference signal S5 of the vertical reference frequency f.sub.V of 59.94 Hz. The frequency division ratio setting circuit 15 serves to set the frequency division ratio of the frequency divider 8 and the frequency division ratio in the above described case is selected to be 1/59719. The servo circuit 7 controls the rotation of the motor 5 such that the relative phase relation of the vertical reference signal S5 from the frequency divider 8 with the rotational heads 3a and 3b may be a constant value, i.e. synchronization of the pulse signal S7 from the fixed head 6 with the vertical reference signal S5 from the frequency divider 8 may be established. Meanwhile, the relative positional relation of the magnets 4a and 4b with the fixed head has been determined such that the pulse signal S7 is obtained from the fixed head 6 when the vertical synchronizing signal recorded at the bottom portion of the video signal track of the magnetic tape is detected by the rotation head 3a or 3b. The above described vertical reference frequency f.sub.V is 59.94 Hz for both of the NTSC system and the 4.43 NTSC system and the accuracy of 0.01 to 0.1% is required. Accordingly, the vertical reference signal S5 is usually obtained through frequency division of the output from the crystal oscillating circuit by means of the frequency divider, as described previously.
The oscillating circuit 10a is adapted to provide the color reference signal S6 from the crystal resonator C2 or C3 connected thereto. The frequency of the crystal resonator C2 is selected to be 3.579545 MHz and that of the crystal resonator C3 is selected to be 4.43361875 MHz. Selection between the crystal resonators C2 and C3 is performed by the switch SW2. The switch SW2 is a manual switch and is structured to be switchable in adaptation to the system of the video tape recorder. More specifically, in the case where it is desired that the video tape recorder operate in accordance with the NTSC system, the crystal resonator C2 is selected, whereas it is desired that the video tape recorder operate according to the 4.43 NTSC system, the crystal resonator C3 is selected. The reproduced signal S1 from the rotational heads 3a and 3b is switched by the switch SW1 and is applied to the NTSC color signal processing circuit 11a or the 4.43 NTSC color signal processing circuit 11b. The switch SW1 is also a manual switch and is adapted to be switchable in a ganged fashion with the switch SW2. More specifically, in the case where it is desired that the video tape recorder should operate according to the NTSC system, the NTSC color signal processing circuit 11a is selected, whereas in the case where it is desired that the video tape recorder should operate in accordance with the 4.43 NTSC system, the 4.43 NTSC color signal processing circuit 11b is selected. The NTSC color signal processing circuit 11a extracts only the color signal from the reproduced signal S1 and processes the color signal to convert the same to a color signal of the NTSC system based on the color reference signal S6 obtained from the oscillating circuit 10a. For example, the color signal of the low frequency region converted color subcarrier frequency f.sub.SL of 629 KHz is converted to a color signal of the color subcarrier frequency f.sub.S of 3.58 MHz. Likewise, the 4.43 NTSC color signal processing circuit 11b also extracts only the color signal from the reproduced signal S1 and processes the color signal to convert the same into a color signal of the 4.43 NTSC system. For example, the color signal of the low region converted color subcarrier frequency f.sub.SL of 627 KHz is converted into a color signal of the color subcarrier frequency f.sub.S of 4.43 MHz. In such a case, if the video tape recorder is to be monitored by connecting the same to an ordinary television receiver, the accuracy of 0.001% to 0.01% is required for the color subcarrier frequency f.sub.S and approximately the same precision is required for the color reference signal S6 obtained from the oscillating circuit 10a. Therefore, a crystal oscillating circuit is usually employed for the color reference signal generating circuit 10.
The brightness signal processing circuit 12 extracts only the FM modulated brightness signal and demodulate the same. The mixing circuit 13 serves to mix the color signal S2 from the NTSC color signal processing circuit 11a or the 4.43 NTSC color signal processing circuit 11b with the brightness signal S3 from the brightness signal processing circuit 12, thereby to provide a composite video signal S4 to the terminal 14. The composite video signal S4 is withdrawn directly or through an RF converter, not shown, to a monitor television receiver.
Meanwhile, for better understanding of the background of the present invention, the servo circuit 7, the NTSC color signal processing circuit 11a and the brightness signal processing circuit 12 will be briefly described. FIG. 2 is a block diagram showing the brightness signal processing circuit. The reproduced signal S1 obtained from the rotational heads 3a and 3b is amplified by a preamplifying circuit 16 and is switched by a head selecting circuit 17 and the output therefrom is applied to an FM equalizing amplifying circuit 18. The signal undergoes correction of the frequency by the FM equalizing amplifying circuit 18 and is amplified by an FM amplifying circuit 19 and the output therefrom is applied to a high-pass filter 20. Only the frequency modulated brightness signal is withdrawn from the high-pass filter 20 and the output therefrom undergoes compensation for a missing signal by a dropout compensating circuit 21 and an amplitude varying component is removed by a limiter 22 and the output therefrom is demodulated by a frequency demodulator 23. The demodulated brightness signal undergoes attenuation of a high frequency region by a deemphasis circuit 24 and a frequency band for accomodating a color signal is secured by a low-pass filter 25, whereupon a noise component is removed therefrom by a noise suppressing circuit 26, whereby the output is obtained as a brightness signal S3.
FIG. 3 is a block diagram of the NTSC color signal processing circuit. The reproduced signal S1 is applied through a preamplifying circuit 27 and a head selecting circuit 28 to a color amplifying circuit 29. In actuality, the preamplifying circuit 27 and the head selecting circuit 28 are shared with the preamplifying circuit 16 and the head selecting circuit 17 shown in FIG. 2. Only a color signal of 629 KHz .+-.500 KHz is extracted and amplified by a low-pass filter in a color amplifying circuit 29. The above described color signal is converted into a signal of a constant magnitude by means of an automatic color control circuit 30 and is applied to a main converter 31, where the signal is frequency converted. A bandpass filter 32 extracts only a difference signal of 3.58 MHz .+-.500 KHz. A compressor circuit 33 attenuates by 6 dB the burst signal which was previously amplified by 6 dB on the occasion of recording, thereby to provide the color signal S2. An automatic phase control circuit 34 comprises a burst gate 34a, a phase comparator 36b, a variable frequency oscillating circuit 34c and a subconverter 34d and is supplied with the color reference signal S6, thereby to compensate for phase variation included in the reproduced signal S1 as wow, flutter or the like during the travel of the magnetic tape 1. An automatic frequency control circuit 35 also compensates for frequency variation included as wow, flutter and the like during the travel of the magnetic tape 1. The structure of the 4.43 NTSC color signal processing circuit 11b is the same as that shown in FIG. 3 and the signal of 5.06 MHz is obtained from the subconverter 34d, while the color signal of 4.43 MHz is obtained from the bandpass filter 32.
FIG. 4 is a block diagram of the servo circuit. The vertical reference signal S5 is differentiated by a differentiating circuit 36 and a constant current charging circuit 37 is responsive to the output from the differentiating circuit 36 to charge a capacitor included therein with a constant current. A sample/hold circuit 38 serves to sample/hold the output voltage from the constant current charging circuit 37 at the timing point when the pulse signal S7 is applied. For example, the more the phase of the pulse signal S7 is delayed as compared with the vertical reference signal S5, the higher the voltage obtained from the sample/hold circuit 38 becomes. The output from the sample/hold circuit 38 is amplified by an amplifier 39 and is withdrawn as a driving signal S8. Accordingly, synchronization of the vertical reference signal S5 with the pulse signal S7 is established.
As described in the foregoing, according to the conventional video tape recorder, the switches SW1 and SW2 are switched in association with the system to be reproduced, whereby either the NTSC system or the 4.43 NTSC system can be reproduced. However, the oscillating circuit 9 and the crystal resonator C1 for providing the vertical reference signal S5 and the NTSC color signal processing circuit 10a and the crystal resonators C2 and C3 for providing the color reference signal S6 are separately provided, which increases the number of the components and accordingly increases the number of manufacturing steps and in addition reduces reliability and economy in cost. Furthermore, since the NTSC system employs frequency interleaving in which the sidebands of the color signal are accurately interleaved between the sidebands of the brightness signal, it is required that the frequency of the vertical reference signal S5 has an accurate predetermined relation with the frequency of the color reference signal S6. Therefore, conventionally it has been necessary to make fine adjustment of the frequencies of both the oscillating circuit 9 and the oscillating circuit 10a, which requires some manual work. Thus, it has been desired that a video tape recorder is provided in which the number of components can be reduced and manual work for adjustment can be dispensed with.